The present invention relates to impellers for centrifugal pumps in general, and more particularly to improvements in radial and/or semiaxial impellers. Still more particularly, the invention relates to improvements in the construction and design of vanes in radial or semiaxial impellers.
Recent types of centrifugal pumps with radial or semiaxial impellers are operated at a relatively high rotational speed. This presents problems in the region of inlet edges of the vanes, primarily due to more pronounced cavitation as a result of increased speed of fluid flow at the eye of the impeller. It has been found that implosion of vapor bubbles at the suction sides of vanes in the region of the respective inlet edges results in rapid and pronounced erosion of the material of the vanes. In many instances, the erosion is so pronounced that it causes a complete breakdown of operation of the pump. Presently known proposals to reduce or eliminate erosion which is attributable to cavitation at the suction sides of vanes in a radial or semiaxial impeller include the provision of means for improving the flow conditions in the eye of the impeller, e.g., by resorting to a larger booster pump or inducer, by resorting to geodetically higher situated vanes, by increasing the pressure in the deaerator or feedwater storage tank of a boiler feed pump above saturation pressure and/or by injection of cold water into the affected regions. A drawback of such conventional proposals is that the provision of aforementioned flow improving means contributes excessively to the bulk, cost and complexity of the fluid flow machine.